Isabel A. A. C. Esteves

The mitigation of carbon dioxide (CO2) emissions requires adsorbent materials with tunable pore structures capable of balancing adsorption capacity and selectivity under postcombustion conditions. In this work, a proof-of-concept IL-assisted double-templating strategy is presented to engineer porosity in IL@MOF-derived carbons. The metal–organic framework (MOF) Cu-BTC was used as both carbon precursor and primary template, while the ionic liquid (IL) [C6MIM][B(CN)4] was used as a secondary sacrificial template at low loadings (1–10 wt %). IL@MOF composites with varying IL contents were prepared, carbonized, and subsequently acid-washed to remove residual copper-containing phases formed during carbonization. This enabled the evaluation of how IL loading influences the resulting carbon pore structure and adsorption behavior. Porosimetric characterization shows that IL incorporation promoted the development of additional (ultra)microporosity while simultaneously reducing total accessible pore volume at higher loadings, strongly influencing gas adsorption behavior. CO2 and N2 adsorption–desorption measurements at 303 K revealed a nonmonotonic dependence of CO2 adsorption capacity on IL loading, with a maximum at 2 wt % IL. At higher IL contents, the reduction in accessible pore volume limited adsorption capacity. In contrast, ideal CO2/N2 selectivity at 1 bar increased progressively with IL loading. These results show that even small amounts of IL can systematically tune pore architecture and adsorption performance in IL@MOF-derived carbons. Overall, IL-assisted double templating was validated as a versatile approach for pore engineering in carbon adsorbents, providing a framework for the rational design of materials for CO2 separation applications.

This study reports a semicontinuous subcritical water extraction assisted by deep eutectic solvents (SWH/DES) for valorizing Vitis vinifera grape pomace. Six DES based on choline chloride with different hydrogen bond donors (glycerol, ethylene glycol, malic, tartaric, lactic, and oxalic acids) were evaluated at 150 °C and 200 bar. The lactic acid DES showed the highest recovery of total phenolics (∼275 mg GAE g–1), flavonoids (∼170 mg CE g–1), and antioxidant capacity (∼1600 µmol TEAC g–1 FRAP). Malic acid DES maximized sugar extraction (∼740 mg g–1), tartaric acid DES enhanced protein recovery (∼40 mg g–1), and ethylene glycol DES favored anthocyanin extraction (∼2.6 mg C3G g–1). Compared to conventional subcritical water, SWH/DES increased bioactive recovery up to fourfold. Extracts exhibited antimicrobial activity against E. coli and S. typhimurium. Sustainability assessment was performed using the Path2Green tool, yielding scores of 0.262 and 0.256, which confirm strong alignment with green chemistry and circular economy principles, demonstrating that SWH/DES is an efficient and sustainable extraction strategy.

Composite sorbent materials (IL@MOF) with a metal-organic framework (MOF) ZIF-8 and [B(CN)₄]⁻-based ionic liquids (ILs) were produced for the first time. Characterization results indicate the successful IL impregnation and conservation of the ZIF-8 crystalline structure and morphology. The data collected from the nitrogen (N₂) physisorption at 77 K suggest that these IL@ZIF-8 materials are nonporous as their textural properties, such as BET specific surface area and total pore volume, are negligible. However, CO₂, CH_4, and N₂ adsorption/desorption measurements in the IL@ZIF-8 composites at 303 and 273 K contradict the N₂ data at 77 K, given that the obtained isotherms are Type I, typical of (micro)porous materials. Their gas adsorption capacity and ultramicroporous volume are in the same order of magnitude as the pristine microporous ZIF-8. The case study [C₆MIM][B(CN)₄] IL revealed a high affinity to both CO₂ and CH₄. This compromised the selectivity performance of its respective composite when compared with pristine ZIF-8. This work highlights the importance of accurate experimental gas adsorption/desorption equilibrium measurements to characterize the adsorption uptake and the porous nature of adsorbent materials.

Carbon dioxide (CO₂) capture has become of great importance for industrial processes due to the adverse environmental effects of gas emissions. Mixed matrix membranes (MMMs) have been studied as an alternative to traditional technologies, especially due to their potential to overcome the practical limitations of conventional polymeric and inorganic membranes. In this work, the effect of using different ionic liquids (ILs) with the stable metal–organic framework (MOF) ZIF-8 was evaluated. Several IL@ZIF-8 composites and IL@ZIF-8 MMMs were prepared to improve the selective CO₂ sorption and permeation over other gases such as methane (CH₄) and nitrogen (N₂). Different ILs and two distinct loadings were prepared to study not only the effect of IL concentration, but also the impact of the IL structure and affinity towards a specific gas mixture separation. Single gas sorption studies showed an improvement in CO₂/CH₄ and CO₂/N₂ selectivities, compared with the ones for the pristine ZIF-8, increasing with IL loading. In addition, the prepared IL@ZIF-8 MMMs showed improved CO₂ selective behavior and mechanical strength with respect to ZIF-8 MMMs, with a strong dependence on the intrinsic IL CO₂ selectivity. Therefore, the selection of high affinity ILs can lead to the improvement of CO₂ selective separation for IL@ZIF-8 MMMs.

Adsorption-based processes using metal-organic frameworks (MOFs) are a promising option for carbon dioxide (CO₂) capture from flue gases and biogas upgrading to biomethane. Here, the adsorption of CO₂, methane (CH₄), and nitrogen (N₂) on Zn(dcpa) MOF (dcpa (2,6-dichlorophenylacetate)) is reported. The characterization of the MOF by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and N₂ physisorption at 77 K shows that it is stable up to 650 K, and confirms previous observations suggesting framework flexibility upon exposure to guest molecules. The adsorption equilibrium isotherms of the pure components (CO₂, CH₄, and N₂), measured at 273–323 K, and up to 35 bar, are Langmuirian, except for that of CO₂ at 273 K, which exhibits a stepwise shape with hysteresis. The latter is accurately interpreted in terms of the osmotic thermodynamic theory, with further refinement by assuming that the free energy difference between the two metastable structures of Zn(dcpa) is a normally distributed variable due to the existence of different crystal sizes and defects in a real sample. The ideal selectivities of the equimolar mixtures of CO₂/N₂ and CO₂/CH₄ at 1 bar and 303 K are 12.8 and 2.9, respectively, which are large enough for Zn(dcpa) to be usable in pressure swing adsorption.

Porous carbon materials, derived from biomass wastes and/or as by-products, are considered versatile, economical and environmentally sustainable. Recently, their high adsorption capacity has led to an increased interest in several environmental applications related to separation/purification both in liquid- and gas-phases. Specifically, their use in carbon dioxide (CO₂) capture/sequestration has been a hot topic in the framework of gas adsorption applications. Cost effective biomass porous carbons with enhanced textural properties and high CO₂ uptakes present themselves as attractive alternative adsorbents with potential to be used in CO₂ capture/separation, apart from zeolites, commercial activated carbons and metal-organic frameworks (MOFs). The renewable and sustainable character of the precursor of these bioadsorbents must be highlighted in the context of a circular-economy and emergent renewable energy market to reach the EU climate and energy goals. This mini-review summarizes the current understandings and discussions about the development of porous carbons derived from bio-wastes, focusing their application to capture CO₂ and upgrade biogas to biomethane by adsorption-based processes. Biogas is composed by 55–65 v/v% of methane (CH₄) mainly in 35–45 v/v% of CO₂. The biogas upgraded to bio-CH₄ (97%v/v) through an adsorption process yields after proper conditioning to high quality biomethane and replaces natural gas of fossil source. The circular-economy impact of bio-CH₄ production is further enhanced by the use of biomass-derived porous carbons employed in the production process.